\tracingonline=2
\tracingcommands=2
\tracingmacros=2
\tracingrestores=2

\showthe\font
\showthe\textfont10

\font\x=cmr10

\showthe\font
\showthe\textfont10

\x

\showthe\font
\showthe\textfont10

\font\y=cmr10 at 20pt

\showthe\font
\showthe\textfont10

\y

\showthe\font
\showthe\textfont10

\font\y=cmr10 scaled 2

\showthe\font
\showthe\textfont10

\y

\showthe\font
\showthe\textfont10

\textfont10=\x

\showthe\font
\showthe\textfont10

\textfont10=\y

\showthe\font
\showthe\textfont10

\x
\textfont10=\font

\showthe\font
\showthe\textfont10

\textfont11=\textfont10

\showthe\font
\showthe\textfont10
\showthe\textfont11

\textfont10=\relax

\showthe\font
\showthe\textfont10

\font\z=cmr10 at 0pt
\showthe\z

\font\z=cmr10 scaled 0
\showthe\z

\catcode`{=1
\catcode`}=2
\newlinechar=`@

\message{~ \fontname\font @}
\message{~ \fontname\x @}
\message{~ \fontname\y @}
\message{~ \fontname\textfont11 @}
\message{~ \fontname\textfont2 @}
\message{~ \fontname\relax @}

\font\z=cmr10 at 20pt
\message{~ \fontname\z @}
\font\z=cmr10 scaled 20
\message{~ \fontname\z @}

\end
